Structural health monitoring technologies have significant application values and wide application prospects in preventing major accidents, improving system safety, reducing economic losses, reducing system maintenance costs, and ensuing successful construction of important engineering projects of China. Ultrasonic guided waves are a kind of ultrasonic waves existing in thin plate structures, such as Lamb waves in a thin plate and ultrasonic guided waves longitudinally and transversely propagated in a pipeline. They can propagate with large distance and have high sensitives to both the inner and surface structural defects. Therefore, the ultrasonic guided waves have been widely used in structural health monitoring.
In the field of structural health monitoring using ultrasonic guided waves, high-resolution damage monitoring technologies are the focus of current researches. The resolution of damage monitoring using ultrasonic guided waves depends on the signal resolution to a large extent, and the signal resolution is directly related to the time-domain and space-domain widths of signal wave packets. In practical applications, due to the dispersive characteristic that phrase/group velocities of ultrasonic guided waves are related to frequencies, time-domain extension easily occurs on the signal wave packets, resulting in a lowered signal resolution. In another aspect, a relatively large distance-domain width of a wave packet in an ultrasonic guided wave signal is also one of main factors that affect the signal spatial resolution.
A provided time-distance domain transformation method improves the signal resolution merely by using dispersion compensation and then recompressing a signal wave packet extended by dispersion effect, without considering the influence caused by that the signal wave packet has a relatively large width in distance domain. Therefore, further improvement of the signal resolution is limited.